The present invention relates generally to an electric instrument amplifier which is used by connecting with an electric music instrument such as an electric guitar. In particular, the present invention relates to an electric instrument amplifier which is designed to emulate the audio characteristics associated with the traditional vacuum-tube-type amplifier.
As semiconductor technology has become more advanced in recent years, the convenience of semiconductor devices, such as transistors and ICs, are increasingly available to be used with amplifiers for electrical instruments. Despite such semiconductor devices, however, vacuum-tube-type amplifiers can output its unique audio output characteristics, and thus, are still strongly popular today in the field of electric instruments and continue to be manufactured and sold on the market in large numbers.
Especially, a guitar amplifier using vacuum-tubes (vacuum-tube type amplifier) has been widely accepted due to its capability of bringing out the distorted sound features of an electric guitar. When the guitar amplifier using the vacuum-tube is set to overdrive, this distortion is synthetically produced through several steps in a pre-amplifier, driver stages of a power amplifier, the power amplifier itself, and matching transformers and speakers in the vacuum-tube type amplifier. Furthermore, a guitar amplifier can obtain an optimum distortion when outputting an extremely high sound volume. This is mainly the result of the additional distortion brought on from the later stages of circuit in the driver of the power amplifier driver. Many professional guitarists wish to use this vacuum-tube type amplifier for this reason.
However, as is well known in the art, in comparison to the semiconductor devices, the vacuum-tube type amplifier has several disadvantages such as a short life time with low reliability, storage inconvenience because it is large and heavy, high power and heat dissipation, and needs of high voltages, as well as it is relatively expensive. Using the vacuum-tube type amplifier will therefore be accompanied by such risks and drawbacks.
In order to resolve these problems, several inventions have been made to emulate the output characteristics of the vacuum-tube type amplifier by using semiconductor devices. Electric amplifiers using such technologies disclosed in the inventions have been in practical use.
An example of such inventions is the U.S. patent application Ser. No. 09/200,102 (hereafter be referred to as xe2x80x9cprior art 1xe2x80x9d). In this technology, the output signal of an amplifier that is structured by a small number of vacuum-tubes is amplified by a semiconductor circuit to create an amplifier capable of outputting a high sound volume, as if it were coming from a large number of vacuum-tubes. By doing so, the characteristics of the vacuum-tube type amplifier can be emulated.
However, the technology described in the prior art 1 is not structured to be in direct use with an electric instrument, like an electric guitar. Rather, it is designed to amplify the output of the later stage of the vacuum-tube type amplifier. Namely, the technology shown in the prior art 1 is not able to directly connect to an electric instrument.
In other words, the majority of such guitar amplifiers or guitar effect devices that use the vacuum-tube method are not integrated into one system. Thus, in an actual use, by connecting such guitar amplifiers or guitar effect devices through cables, and changing the connections or routings during the performance, changes among various tone settings are achieved in the performance. This conventional method produces a problem for guitarists during live performances and/or recordings, because an external switching system is required for changing the connections of the guitar amplifiers or guitar effect devices based on predetermined timings during the performance. This in turn increases the number of surrounding equipment, and can cause problems such as imperfect cable connections.
On the other hand, because of the recent development in the digital signal processing technology, such a digital technology is now frequently used in the electric music instruments. For example, digital effects such as digital emulators, equalizers, and reverberators, or digital speaker simulators which recreate speaker characteristics, have been in use with incorporating DSP (Digital Signal Processor) since the 1980s in order to reproduce the distortion characteristics of the pre-amplifier portion of the vacuum-tube type guitar amplifier.
These music devices, using the digital signal processors (DSP), can control the positioning, connections, and tone settings for each component (digital emulator, digital effect, and digital speaker simulator) by monitoring through liquid crystal displays. In addition, these music devices using the DSP, can receive information regarding switching timings through, for example, MIDI (Musical Instrument Digital Interface) signals. Thus, the data regarding the positioning, connections and tone settings stored in a memory in the music device can be automatically changed with use of a micro-controller.
Therefore, without the requirement of an external switching system, a guitarist can quickly change and control various tone settings by using the aforementioned devices having the DSP therein, power amplifier, and speaker cabinet. This method is also able to avoid the problems such as imperfect cable connections and to minimize the number of surrounding equipment.
Another example of conventional technology regarding the electric amplifier is capable of directly connecting to an electrical instrument. Such as an electric guitar is shown in the U.S. Pat. No. 5,789,689, titled xe2x80x9cTube Modeling Programmable Digital Guitar Amplification Systemxe2x80x9d (hereafter be referred to as xe2x80x9cprior art 2xe2x80x9d). This patent explains how the guitar amplifier is placed under one housing system, and its technique on how to emulate the output characteristics of a vacuum-tube type amplifier.
The prior art 2 also explains that, after changing the music signals from the electric guitar to digital signals, the digital guitar amplification system adds the distortion property unique to the vacuum-tube type amplifier to the digital signals with use of a pre-amplifier effect, a nonlinear effect, and a linear effect. Then, the digital guitar amplification system converts the digital signals to analog signals and outputs as music signals.
In the prior art 2, however, since the digital guitar amplification system utilizes a nonlinear function produced by a digital signal processor in the course of emulating the vacuum-tube type amplifier, it can actually only emulate the pre-amplifier portion of the vacuum-tube type amplifier. There is no indication in this patent that the power amplifier portion of the vacuum-tube type amplifier has been devised. Hence, the distortion property of the vacuum-tube type amplifier is not being truly emulated. Accordingly, the digital guitar amplification system mentioned in the prior art 2 is not able to reproduce the vacuum-tube type amplifier with high fidelity.
It is, therefore, an object of the present invention to provide an electric instrument amplifier which has an integral form and can directly connect to an electric instrument such as an electric guitar to produce the distortion characteristics of a vacuum-tube type amplifier with use of digital technologies.
It is another object of the present invention to provide an electric instrument amplifier which amplifies music signals from the electric instrument with use of a minimum number of vacuum-tubes to produce output audio signals as though the audio signals were produced by many vacuum-tubes.
It is a further object of the present invention to provide an electric instrument amplifier which amplifies music signals from an electric instrument while adding the distortion property of the vacuum-tube type amplifier with high fidelity and with low cost.
In a preferred embodiment, the electric instrument amplifier of the present invention includes an A/D converter which converts an audio signal from an electric instrument to a digital signal. The digital signal is supplied to a digital signal processor. A boost effect in the digital signal processor amplifies the audio signal to a desired level, then adds the distortion to the audio signal through a pre-amplifier simulator. Processes such as equalization are performed on the audio signal which is also added with other effects such as ambience by a MOD/AMB effect.
The audio signal processed through the digital signal processor is converted to an analog signal by a D/A converter, and then supplied to a tube amplifier through a FET driver. The tube amplifier has a push-pull structure having a first vacuum-tube and a second vacuum tube and amplifies the audio signal from the D/A converter by push-pull operations. The amplified audio signal is then supplied to the virtual power circuit through a transformer.
The virtual power circuit is equipped with a current amplifier and a voltage amplifier, which creates a relationship of xe2x80x9cAc*Av=xe2x88x92Kxe2x80x9d, where K is constant, Ac is current gain, and Av is voltage gain. Therefore, this makes the load impedance seen from the tube amplifier and the load impedance seen from the virtual power circuit substantially identical to one another. Accordingly, the audio signal generated by the virtual power circuit has the same output characteristics of the tube amplifier while a power level of which is either amplified or attenuated.
According to the present invention, the electric instrument amplifier can produce the audio signal which sounds as through it were created by using many vacuum-tubes although using only a minimum number of vacuum-tubes. The electric instrument amplifier of the present invention is advantageously used when being connected to electric instruments such as an electric guitar in a live performance. Further, since the entire device is formed in one housing, the number of equipment can be minimized and problems of cable connections can be avoided.